Through disease or injury, the laminae, spinous process, or articular processes of one or more vertebral bodies can become damaged, such that the vertebrae no longer articulate or properly align with each other. This can result in an undesired anatomy, loss of mobility, and pain or discomfort. For example, spinal stenosis, as well as spondylosis, spondylolisthesis, and other degenerative phenomena may cause back pain, especially lower back pain, such as in the lumbosacral (L4-S1) region. Such phenomena may be caused by a narrowing of the spinal canal by a variety of causes that result in the pinching of the spinal cord and/or nerves in the spine.
The prior art has many spinal prostheses designed to help the patient with various back problems. For example, published PCT Patent Application WO 2005/044152, assigned to the present assignee, describes a spinal prosthesis having a unitary body with three or more attachment points attachable to spinal structure. The unitary body includes a flexure assembly positioned between first and second attachment members, wherein flexure of the flexure assembly permits movement of the first attachment member relative to the second attachment member. The flexure assembly may be adapted to flex omnidirectionally. A plurality of pedicle screws (e.g., polyaxial pedicle screws with polyaxial swivel heads) may be attached to or integrally formed with the spinal prosthesis.
As another example, U.S. patent application Ser. No. 11/019,276, assigned to the present assignee, describes a spinal prosthesis that may be adjusted in-situ, such as but not limited to, being adjusted to a desired lordotic angle. The prosthesis may include a pair of spinal prosthetic members movably attached to one another with a fastening device. The fastening device has a non-tightened position which permits spatial movement of the spinal prosthetic members with respect to one another at a desired orientation, and a tightened position which fixes the first and second spinal prosthetic members at the desired orientation. The spinal prosthetic members may be pivotable with respect to one another to define an angle therebetween that corresponds to a lordotic angle between spinal structures.